The original due date of April 15, 2021 was only extended for individuals, not estates or trusts filing Form 1041. The extension request will allow a 5 1/2 month extension for Form 1041 which will make the due date September 30, 2021. The information stating the length of the extension is outlined in the Form 7004 instructions.
(The article linked in your question is incorrect as far as the number of months allowed, but the due dates are accurate. It will be submitted for corrections.)